public static Stream <T> periodic(TimeSpan period,
Func <int, T> computation = null)
{
Timer timer = default;
int computationCount = 0;
StreamController <T> controller = null;
// Counts the time that the Stream was running (and not paused).
Stopwatch watch = new Stopwatch();
Action sendEvent = () => {
watch.reset();
T data = default;
if (computation != null)
{
try {
data = computation(computationCount++);
}
catch (Exception e) {
controller.addError(e, e.StackTrace);
return;
}
}
controller.add(data);
};
Action startPeriodicTimer = () => {
D.assert(timer == null);
timer = Timer.periodic(period, (object timer1) => {
sendEvent();
return(null);
});
};
// the original code new an abstract class
controller = StreamController <T> .create(
sync : true,
onListen : () => {
watch.start();
startPeriodicTimer();
},
onPause : () => {
timer.cancel();
timer = null;
watch.stop();
},
onResume : () => {
D.assert(timer == null);
TimeSpan elapsed = watch.elapsed;
watch.start();
timer = Timer.create(period - elapsed, () => {
timer = null;
startPeriodicTimer();
sendEvent();
});
},
onCancel : () => {
if (timer != null)
{
timer.cancel();
}
timer = null;
return(Future._nullFuture);
});
return(controller.stream);
}
